Comparative effect of dopamine and quinpirole on melatonin content and cAMP accumulation in retinas excised at 12:00 noon and 12:00 midnight
| cAMP | Melatonin | |||
|---|---|---|---|---|
| 12:00 noon | 12:00 midnight | 12:00 noon | 12:00 midnight | |
| pmol/mg protein | ng/mg protein | |||
| Control | 13 ± 1.5 | 23 ± 1 | 0.194 ± 0.01 | 0.840 ± 0.06 |
| Dopamine | 30 ± 2.52-160 | 34 ± 1.52-160 | 0.130 ± 0.012-160 | 0.800 ± 0.05 |
| Quinpirole | 4.9 ± 0.42-160 | 20 ± 1 | 0.100 ± 0.0072-160 | 0.780 ± 0.05 |
Hamsters were sacrificed at 12:00 noon or midnight, and retinas were incubated under light or darkness, respectively, in the presence or absence of dopamine (100 μM) or quinpirole (10 μM) as described inMaterial and Methods. Dopamine significantly increased cAMP accumulation at 12:00 noon and midnight, and it decreased melatonin content only at midday. Quinpirole significantly decreased both melatonin content and cAMP levels only at midday. Data are mean ± S.E. values (n = 15 animals per group).
↵2-160 P < .01 by Dunnett's test. Control levels of both cAMP and melatonin were significantly higher at midnight than at midday (P < .01, Student's ttest).